UNS K94610 / ASTM F15 / Kovar Alloy

Kovar (Alloy K) is a nickel-iron-cobalt controlled-expansion alloy containing 29% nickel. Its coefficient of expansion, which decreases with rising temperature to the inflection point, matches the expansion rate of borosilicate glasses and alumina ceramics. Alloy K is used for glass-to-metal seals in applications requiring high reliability or resistance to thermal shock. UNS K94610 is used for high-power transmitting valves, transistor leads and headers, integrated-circuit lead frames, and photography flash bulbs.

 

UNS K94610 chemical composition is controlled within narrow limits to ensure precise and uniform thermal expansion and mechanical characteristics. These properties make it an ideal alloy for use in high integrity glass-to-metal and ceramic-to-metal seals, particularly where the application requires resistance to thermal shock.

 

Kovar is often used for the manufacture of hermetic seals with both the harder Pyrex or borosilicate glasses and alumina-type ceramic materials. The alloy finds extensive application in the production of transistors and diodes for lids and closures in a variety of hybrid electronic circuit packages and also in the manufacture of microwave tubes. In order to achieve optimum conditions for subsequent sealing operations, it is recommended to first condition the material using a thermal degassing / decarburizing treatment carried out in a moist hydrogen atmosphere. This is then normally followed by a controlled oxidizing heat treatment in order to create a tightly adherent surface oxide film of optimum nature and thickness.